Bleomycin, an anti-neoplastic agent, is known to produce pulmonary fibrosis as a toxic complication of its use. This fibrosis appears to be the result of a free radical effect, mediated by the formation of an iron-bleomycin complex. The present study shows that the pulmonary toxicity of bleomycin in rats is mitigated by the administration of ICRF-187, a bis-diketopiperazine that functions as an iron chelator.